Very few people will argue about the necessity of sleep. We all have felt that "sleepy" feeling and have thankfully retired to a "good night’s sleep." As we awaken in the morning, we hope to feel rested and energized. It is easy to think that our body systems have also rested quietly during the night, regaining strength for the next day.

With some of the body systems, that is true. For example, heart rate slows at the onset of sleep. Blood pressure usually lowers soon after going to sleep.

However, sleeping does not mean that all of the body systems slow down and rest at night. New technology that detects brain activity us revealing exciting insights into the process of sleep.

To better understand the body’s activities during sleep, let’s review the stages of sleep. Human sleep is divided into two basic phases—rapid eye movement sleep and non-rapid eye movement sleep. Each of these phases has unique characteristics.

The non-rapid eye movement (NREM) occurs when sleep begins and continues during most sleep time. A person first drifts from a state of wakefulness into a drowsy state, followed by true, quiet sleep. NREM sleep continues throughout the night and includes changes in the depth of sleep, sometimes shallow, sometimes deeper.

Rapid eye movement (REM) sleep is a normal stage of sleep characterized by rapid eye movements, low muscle tone, and changes in brain activity. This stage of sleep typically occupies about 20 to 25 percent of total sleep time for adult humans. An adult usually experiences about 4 to 5 periods of this stage of sleep during a normal night of sleep (totaling 90 to 120 minutes).

Brain Active During Sleep

The human brain is active during sleep, especially during rapid eye movement sleep. In fact, more brain activity occurs during sleep than when a person is awake.

Sleep and the cycles that occur during sleep play a critical part in the development of long-term or permanent brain cell circuitry. This process is essential for learning and memory during the lifetime of an individual.

Of course, a person has to begin the process by acquiring memories. This is accomplished by sensory input-seeing, hearing, feeling, tasting, moving and emotions. Brain stimulation from this sensory input is stored in short-term memory patterns, located in various brain "storage" areas.

During NREM sleep, the sensory input is moved from the "storage" areas of the brain to other brain areas which actively sort the memory patterns. Weak and unimportant signals and stimuli are eliminated. Important, strong, prominent images and signals are collected in special areas of the brain, where they are organized, integrated and related. This phase is referred to as the consolidation phase.

A third phase of learning and memory occurs during REM sleep. The short-term memory circuits that were created when the person was awake and consolidated during NREM sleep are reactivated. Special brain wave activity returns the organized and integrated neurosensory memory content back to the brain "storage" areas. The memory content now becomes long-term organized memory circuits which are located in appropriate areas of the brain where they can be recalled or used to build more complex memory patterns. This is referred to as "the learning process."

Your brain is definitely not resting during sleep! In fact, you can see how important sleep is for the brain to carry out effective learning processes.